Effects of deforestation on headwater stream fish assemblages in the Upper Xingu River Basin, Southeastern Amazonia

ABSTRACT The expansion of the Amazonian agricultural frontier represents the most extensive land cover change in the world, detrimentally affecting stream ecosystems which collectively harbor the greatest diversity of freshwater fish on the planet. Our goal was to test the hypotheses that deforestation affects the abundance, richness, and taxonomic structure of headwater stream fish assemblages in the Upper Xingu River Basin, in Southeastern Amazonia. Standardized sampling surveys in replicated first order streams demonstrated that deforestation strongly influences fish assemblage structure. Deforested stream reaches had twice the fish abundance than reference stream reaches in primary forests. These differences in assemblage structure were largely driven by increases in the abundance of a handful of species, as no influence of deforestation on species richness was observed. Stream canopy cover was the strongest predictor of assemblage structure, possibly by a combination of direct and indirect effects on the provision of forest detritus, food resources, channel morphology, and micro-climate regulation. Given the dynamic nature of change in land cover and use in the region, this article is an important contribution to the understanding of the effects of deforestation on Amazonian stream fish, and their conservation.

摘要 亚马逊农业开发前沿的扩张是全球规模最大的土地覆盖变化事件，正对溪流生态系统造成不利影响——这些生态系统共同栖息着全球物种多样性最为丰富的淡水鱼类类群。本研究旨在验证以下假说：森林砍伐会影响亚马逊东南部上欣古河流域源头溪流的鱼类群落丰度、物种丰富度及分类学结构。对重复布设的一级溪流（first order streams）开展标准化采样调查后发现，森林砍伐对鱼类群落结构具有显著影响。经森林砍伐的溪流河段的鱼类丰度，是原生林参照溪流河段的两倍。鱼类群落结构的这类差异，主要由少数物种的丰度上升所驱动，研究未观测到森林砍伐对物种丰富度存在显著影响。溪流冠层覆盖度是预测鱼类群落结构的最强因子，其可能通过直接与间接的双重作用，影响森林碎屑供给、食物资源供应、河道形态及微气候调控。鉴于该区域土地覆盖与利用变化的动态特性，本研究对于阐明森林砍伐对亚马逊溪流鱼类的影响及其保护工作具有重要意义。